The present application claims priority to German Patent Application Serial No. P 197 40 144.9; filed Sep. 12, 1997.
The invention relates to a connection of a metal pipe with a metal sleeve by means of cold-pressing deformation and a method for producing such a pipe connection.
In the field of relatively high-pressure hose connections it is known to use double sleeves as connecting elements, with an outer sleeve and an inner sleeve connected at the end. The outer sleeve is provided with tooth-shaped, circumferentially extending ridges along its inner wall. For assembly with the end of a hose, the connecting element is pushed all the way onto the hose end and the outer shell is pressed onto the hose shell by means of an assembly device. The assembly device is a conical tool that comprises several segments and is axially shifted in an inner cone. Pressing the outer shell causes the teeth to penetrate the hose surface all the way to the metallic hose core. This connects the sleeve with the hose and provides a seal with the sleeve.
For a push-type connection of two metal pipes, EP 0 470 902 discloses the use of a sleeve provided with axial ribs along its inner wall. The sleeve is made of an alloy with shape memory effect. To connect two pipes, the sleeve is guided over the pipe ends and the shape memory effect is triggered by heat treatment, which causes the sleeve to shrink onto the pipe ends and thus to create a tight connection.
The object of the present invention is to use cold-pressing deformation to create a pipe connection that represents a form-fit connection, provides a tight seal and high pressure resistance, offers a wide variety of connection possibilities with all readily available pipe connections, and can be produced inexpensively.
In the initially-mentioned connection of a metal pipe with a metal sleeve, this object is attained with a pipe limit stop on the inside shell of the metal sleeve and deformations on the inside shell of the portion of the sleeve that is to be connected with the pipe end. Cold-pressing deformation using appropriate pressure applied by an assembly tool causes these deformations to be pressed into the shell of the pipe and thus produces a tight connection between the pipe shell and sleeve.
In one embodiment of the invention, the deformations of the inside shell are formed as ribs disposed parallel to each other and extending circumferentially around the axis of the sleeve. When pressure is applied, the ribs and the pipe shell are deformed to produce a metallic connection. Hermetically-sealed spaces remain between the ribs so as to create a pressure-resistant and pressure-tight connection of a plurality of metal seals that are arranged one behind the other in the direction of the pipe axis.
In an advantageous modification of the invention, the deformations and/or axial ribs are spaced at varying distance from each other so that the hermetically-sealed spaces arranged one behind the other are also differently sized.
It is particularly advantageous if the inside wall of the sleeve is provided with a recess to receive a sealing ring to support the metallic seals and to enhance leakage protection. Such a recess is advantageously provided in front of the first rib of the sleeve in the area of the pipe limit stop to further enhance the resistance to pressure. An elastomer ring is a particularly suitable sealing element.
In a further modification of the invention, the deformations and ribs differ in height (i.e., radial projection) before assembly. During cold-pressing deformation, the deformations and ribs are pressed into the pipe shell at a different rate while being deformed at the same time to create a form-fit connection. This embodiment requires a continuously increasing force during the pressing process since an increasing number of ribs or deformations enter into the pressing range. Only when all deformations or ribs have been subjected to the pressing process, the force increases steeply which indicates that the assembly is complete.
In a further embodiment, the sleeve is provided with a tapered entry area, adjacent to which there is a plurality of deformations and/or ribs. This enhances assembly when the pipe is inserted into the sleeve. Significant, however, is the fact that the tapered entry area substantially dampens any oscillations transferred by the pipe.
In a further embodiment, the deformation of the inside shell of the sleeve is formed as a convex curvature to create a frictionally-engaged connection. To increase the coefficient of friction, the surface of the convex curvature is roughened.
To further increase the coefficient of friction, the surface of the convex curvature is coated with a microencapsulated adhesive. In a modification thereto, the inside surface of the sleeve may also be coated with a hard granulate.
In a still further embodiment, the metal sleeve is combined with a screwed pipe connection.
In principle, the connection according to the invention may be combined with any of the screwed pipe connection systems that are readily-available on the market.
According to the method for creating the pipe connection, the metal sleeve to be connected with the pipe end is pushed onto the pipe end up to the limit stop and then subjected to a compressive force such that the sleeve deformations and/or ribs are plastically deformed while causing the pipe to be deformed. For this purpose, commercially available hose presses may be used, but their working pressure must be correspondingly enhanced, or else special tool inserts must be used.